Fuel for solid electrolyte type fuel cell and solid electrolyte type fuel cell and a method of using it

ABSTRACT

The present invention provides a solid electrolyte type fuel cell that can control a cross-over, and implements the high fuel efficiency and the high output of the fuel cell.  
     A substance is dissolved to a fuel  124,  and does not permeate a solid polymeric electrolyte film  114.  Because of this, on an interface between the solid polymeric electrolyte film  114  and the fuel  124  in a fuel electrode  102 , an osmotic pressure in a direction from an oxide agent electrode  108  to a fuel electrode  102  is generated. Because of this, the water movement from the fuel electrode  102  side to the oxidizing agent electrode  108  side is controlled, and the cross-over of the fuel is controllable.

TECHNICAL FIELD

The present invention relates to a fuel for solid electrolyte type fuelcell and a solid electrolyte type fuel cell and a method of using it.Particularly, it relates to the fuel for solid electrolyte type fuelcell and the solid electrolyte type fuel cell and the method of usingit, which are capable of controlling a cross-over of the solidelectrolyte type fuel cell, and capable of implementing a high fuelefficiency and a high output of the fuel cell.

BACKGROUND OF THE ART

The solid electrolyte type fuel cell is an apparatus for generatingelectricity from the electrochemical reaction by supplying an oxygen toan oxidizing agent electrode, and by supplying a hydrogen to a fuelelectrode, comprising a solid polymeric electrolyte film such asperfluorosulfonate film as the electrolyte, and the fuel electrode andthe oxidizing agent electrode are joined to both faces of this film.

The following electrochemical reaction is taking place in eachelectrode.H₂→2H⁺+2e⁻  Fuel electrode:½O₂+2H⁺+2e⁻→H₂O   Oxidizing agent electrode:

From this reaction, the solid electrolyte type fuel cell can achieve ahigh output of more than 1 A/cm2 at the normal temperature and pressure.

The fuel electrode and the oxidizing agent electrode are comprised ofthe mixture of solid polymeric electrolyte and carbon powders supportingcatalyst material. In general, this mixture is coated on top of anelectrode substrate such as carbon paper, becoming a gas diffusion layerof the fuel. The solid polymeric electrolyte film is sandwiched by thetwo electrodes, and it is heat compressed; and the fuel cell isconfigured accordingly.

In the fuel cell under this configuration, a hydrogen gas supplied tothe fuel electrode reaches the catalyst by passing through the pores ofthe electrode, the electrons are released, and the hydrogen ion isformed. The released electrons are guided to an outer circuit through asolid electrolyte and carbon powders in the fuel electrode, and flowninto the oxidizing agent electrode from the outer circuit.

On the other hand, the hydrogen ion generated at the fuel electrodereaches the oxidizing agent electrode through the solid polymericelectrolyte in the fuel electrode and the solid polymeric electrolytefilm positioned in between the two electrodes. As indicated in the abovereaction equations water is generated by reacting with the electronsflown in from the outer circuit and the oxygen supplied to the oxidizingagent electrode. As a result of this, in the outer circuit, the electronflows from the fuel electrode towards the oxidizing agent electrode, andthe electric power is taken out.

As above, the fuel cell with hydrogen as its fuel has been described,however, in recent years, a fuel cell using a liquid organic fuel suchas methanol is extensively being researched and developed.

Well-known fuel cells using the liquid organic fuel are those thatpurifies the liquid organic fuel to a hydrogen gas to be used as a fuel,and those represented by a direct methanol type fuel cell which directlysupplies the liquid organic fuel to the fuel electrode withoutpurifying.

Among them, the fuel cell that directly supplies the liquid organic fuelto the fuel electrode without purifying, it has the configuration thatcan supply the liquid organic fuel directly to the fuel electrode, andit does not require an apparatus such as purifier. Therefore, it has themerit in the cell configuration being simple, and the whole apparatuscan be made small. Moreover, in comparison to the gas fuels such ashydrogen gas and hydrocarbon gas, the liquid organic fuel has anadvantage of facilitating a safe transport.

In general, the fuel cell using the liquid organic fuel utilizes thesolid polymeric electrolyte film made of a solid polymeric ion exchangeresin as the electrolyte. Herewith, for the fuel cell to function, thehydrogen ion must move from the fuel electrode to the oxidizing agentelectrode through this film. Since the movement of hydrogen ionaccompanies the movement of water, therefore, a certain amount ofmoisture must be contained in the film.

However, in the case of using the liquid organic fuel such as methanolespecially having a high hydrophilic property to water, the liquidorganic fuel is diffused in the solid polymeric electrolyte filmcontaining water, and furthermore, it reaches to the oxidizing agentelectrode to cause a phenomenon called cross-over. If the cross-over isgenerated, the liquid organic fuel for supplying electrons in the fuelelectrode is oxidized at the oxidizing agent electrode, and it is noteffectively utilized as the fuel. Because of this, the voltage andoutput are decreased which causes a decline in the fuel efficiency.

DISCLOSURE OF THE INVENTION

Accordingly, the present invention aims to provide a fuel for solidelectrolyte type fuel cell capable of controlling the cross-over.

Furthermore, the present invention aims to provide a fuel for solidelectrolyte type fuel cell capable of the high fuel efficiency and thehigh output of the solid electrolyte type fuel cell.

Furthermore, the present invention aims to provide a method of using thesolid electrolyte type fuel cell capable of controlling the cross-over.

Furthermore, the present invention aims to provide the method of usingthe solid electrolyte type fuel cell having the high fuel efficiency andthe high output.

Furthermore, the present invention aims to provide a solid electrolytetype fuel cell capable of controlling the cross-over. Furthermore, thepresent invention aims to provide a solid electrolyte type fuel cellhaving the high fuel efficiency and the high output.

According to one aspect of the present invention solving these topics, afuel for a fuel cell having a solid electrolyte film, wherein the fuelcomprises a liquid organic fuel, and a compound excluding sulfuric aciddissolved in the liquid organic fuel that does not permeate the solidelectrolyte film.

As a solid electrolyte film to be used in the solid electrolyte typefuel cell, in general, a solid electrolyte film having a high hydrogenion conductivity, represented by Nafion®, is utilized. The high hydrogenion conductivity of the solid electrolyte film such as this, isgenerated by inclusion of water in the solid electrolyte, on the otherhand, due to this moisture content, the liquid organic fuel such asmethanol facilitates dissolution to water, and urges the occurrence ofcross-over by reaching to the oxidizing agent electrode.

Henceforth, the present invention focuses on an osmotic pressuregenerated at an interface between a solid electrolyte film and a liquidorganic fuel supplied to a fuel electrode, and a substance that does notpermeate the solid electrolyte film is dissolved in the fuel as acompound. The solid electrolyte film permeates water, on the other hand,it functions as a partial film that does not permeate the compound.Because of this, at the interface between the solid electrolyte film andthe liquid organic fuel, an osmotic pressure in a direction from theoxidizing agent electrode to the fuel electrode is generated. Therefore,the water movement from the fuel electrode side to the oxidizing agentside is controlled, such that the movement of liquid organic fuel to theoxidizing agent side is also reduced. That is, the cross-over can bedecreased.

Herewith, conventionally, a fuel cell technology for generatingelectricity by supplying a substance other than the fuel to the fuelelectrode accompanied by the fuel did exist. For example, Japaneseexamined patent publication No. HEI 8-21396 discloses a fuel celltechnology for generating electricity by supplying a fuel containingmethanol and sulfuric acid. The sulfuric acid is supplied as theelectrolyte solution for transporting the hydrogen ion. Henceforth, inorder to maintain the hydrogen ion conductivity, a concentration of thesulfuric acid is set more than a certain value, and the fuel must bekept strongly acidic. Because of this, the corrosion of metalliccomponents in the cell such as collector and metallic seal is readilyprogressed, and the long-term reliability of the cell is not sufficient,and the cell may be damaged. Moreover, when the cell is damaged and thesulfuric acid came in contact to the human body, since the sulfuric acidis non-volatile, it causes skin structure damages and inflammations, anda bad influence is of a great concern. The present invention attempts tosolve the problem by utilizing a compound other than the sulfuric acidas the compound to be dissolved in the liquid organic fuel. Moreover,according to another aspect of the present invention, in the fuel forsolid electrolyte type fuel cell, the compound is preferablynon-electrolyte.

In the case of operating the fuel cell by serially connecting aplurality of unit cells for obtaining a high electro-motive power, whenelectrolyte is added to the fuel, water electrolysis is generated, andthe obtained output is declined. Under such circumstance, by selectingthe non-electrolyte as the compound, the water electrolysis iscontrolled, and an osmotic pressure is generated.

Moreover, according to another aspect of the present invention, in thefuel for solid electrolyte type fuel cell, the compound is preferably anorganic compound except for the liquid organic fuel.

Since an organic compound except for the liquid organic fuel is added tothe fuel for solid electrolyte type fuel cell, an electric resistance ofthe fuel is maintained high. Because of this, inside the fuel cell, thewater electrolysis is controlled, and the osmotic pressure is generated.The organic compound is preferably at least one type selected from sugargroups, alcohol groups and amine groups. The compound is either one ofthe sugar groups, alcohol groups and amine groups, therefore, it isneutral to weakly basic. Henceforth, the compound does not corrode themetallic components inside the fuel cell, and the long-lastingreliability of the fuel cell is secured. Moreover, the sugar groups,alcohol groups, and amine groups are electrochemically stable,therefore, a stable osmotic pressure is effectively generated.

Moreover, according to another aspect of the present invention, thecompound is preferably a strong electrolyte excluding the sulfuric acid.

The strong electrolyte is dissolved in a liquid organic fuel in thedissipated condition into positive ion and negative ion. The negativeion cannot permeate through a solid electrolyte film. This is becausethe solid electrolyte film comprises a lot of negatively chargedfunctional groups such as sulfonic acid group for supporting thehydrogen ion conductivity. The negative ion electrically repels fromthese functional groups. Henceforth, an osmotic pressure is generated atan interface between a fuel and a solid electrolyte film.

Moreover, if a strong electrolyte is selected, it becomes possible toobtain a high osmotic pressure at a small amount of addition of thestrong electrolyte. For example, in the case of dissolving a singlemolecule of Na2SO4 in the fuel, the Na2SO4 molecule is electrolyzed intotwo Na+ ions and one SO42− ion. Because of this, an osmotic pressure ofthree molecules is provided from a single Na2SO4 molecule.

Moreover, by dissolving an electrolyte to a fuel, the conductivity ofthe fuel is improved. The inner resistance loss of the fuel cell isreduced from this, which can contribute to the improved output of thefuel cell.

The sulfuric acid is a strong electrolyte, however, being stronglyacidic and non-volatile, as described previously, form the notions ofinfluence on human and securing long-lasting reliability of the cell, itis exempted as the strong electrolyte in the present invention.

Moreover, according to another aspect of the present invention, in thefuel for solid electrolyte type fuel cell, the strong electrolyte ispreferably chloride, nitrate, and sulfate.

By selecting the above compound as the strong electrolyte, the fuel canbe maintained neutral, and the corrosion of the metallic componentsinside the fuel cell is not generated so that the durability of fuelcell is unaffected, capable of resolving the problem of cross-over.

Moreover, according to another aspect of the present invention, in thefuel for solid electrolyte type fuel cell, the compound concentration ispreferably ranging from 1 mmol/L to 1 mol/L.

By setting the compound concentration ranging from 1 mmol/L to 1 mol/L,a sufficient osmotic pressure necessary to reduce the cross-over isgenerated.

Moreover, according to another aspect of the present invention, the fuelfor solid electrolyte type fuel cell preferably has a pH value rangingfrom 4 to 8.

By setting the pH value of the fuel for solid electrolyte type fuel cellin the range of 4 to 8, a bad influence to the solid electrolyte filmand corrosion of metallic components inside the fuel cell are prevented,and can contribute to the stable fuel cell operation.

Moreover, according to another aspect of the present invention, a methodof using the solid electrolyte type fuel cell comprising a fuelelectrode, an oxidizing agent electrode, and a solid electrolyte filmpositioned in between the fuel electrode and the oxidizing agentelectrode, wherein a fuel includes a liquid organic fuel and a compoundexcluding the sulfuric acid dissolved in the liquid organic fuel withoutpermeating the solid electrolyte film, wherein the fuel is supplied tothe fuel electrode.

The problem of cross-over is resolved by this method, and a favorableand stable long-lasting cell efficiency is implemented.

Moreover, according to another aspect of the present invention, thesolid electrolyte type fuel cell comprises a fuel electrode, anoxidizing agent electrode, a solid electrolyte film positioned inbetween the fuel electrode and the oxidizing agent electrode, and a fuelsupplied to the fuel electrode, wherein the fuel includes a liquidorganic fuel and a compound excluding the sulfuric acid dissolved in theliquid organic fuel without permeating the solid electrolyte film.

In the solid electrolyte type fuel cell of the present invention, thecross-over of the liquid organic fuel is controlled, therefore, theoutput is high and the cell efficiency is favorable.

Moreover, according to another aspect of the present invention, itfurther includes a supplying step for supplying the fuel for solidelectrolyte type fuel cell to the fuel electrode.

The fuel cell related to the present invention has a fuel electrode, anoxidizing agent electrode, and a solid electrolyte film sandwichedbetween the fuel electrode and the oxidizing agent electrode, and adoptsconfiguration which directly supplies a liquid organic fuel to the fuelelectrode, which is so-called direct type fuel cell. The direct typefuel cell has the high cell efficiency, and has advantages such ascapable of attempting reduction in space because the purifier is notnecessary. Yet, the problem of cross-over of the liquid organic fuelsuch as methanol remains. According to the present invention, theproblem of cross-over is solved, and favorable and stable long-lastingfuel efficiency is implemented.

Moreover, according to another aspect of the present invention, thesolid electrolyte type fuel cell further includes preferably a recyclingstep for recycling the used fuel expelled from the fuel electrode, aconcentration adjusting step for adjusting concentrations of thecompound and the liquid fuel in the used fuel recycled at the recyclingstep, and a transporting step for transporting the used fuel havingadjusted the concentration at the concentration adjusting step to thesupplying step.

The fuel cell of the present invention can reuse the liquid organic fuelunconsumed at the fuel electrode, so that the liquid organic fuel isused non-wasted at high efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing one example of theconfiguration of the solid electrolyte type fuel cell according to oneembodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing one example of theconfiguration of the fuel cell according to one embodiment of thepresent invention.

FIG. 3 is a schematic block diagram showing one example of theconfiguration of the fuel supplying system of the fuel cell according toone embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereunder, one embodiment of the present invention shall be describedwith reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing one example of theconfiguration of the solid electrolyte type fuel cell according to oneembodiment of the present invention. A fuel cell 100 comprises aplurality of electrode and electrolyte assemblies 101. The plurality ofelectrode and electrolyte assemblies is electrically connected to oneanother via a fuel electrode side separator 120 and an oxidizing agentelectrode side separator 122. Each of the plurality of electrode andelectrolyte assemblies is comprised of a fuel electrode 102, anoxidizing agent electrode 108, and a solid polymeric electrolyte film114. The fuel electrode 102 is further comprised of a substrate 104 anda catalytic layer 106. The oxidizing agent electrode is furthercomprised of a substrate 110 and a catalytic layer 112.

At a fuel electrode 102 of each electrode and electrolyte assembly 101,a fuel 124 is supplied via the fuel electrode side separator 120.Moreover, at an oxidizing agent electrode 108 of each electrode andelectrolyte assembly 101, an oxidizing agent 126 such as air or oxygenis supplied via the oxidizing agent electrode side separator 122.

The solid polymeric electrolyte film 114 separates the fuel electrode102 and the oxidizing agent electrode 108, and it also has a role ofmoving the hydrogen ion between the two. Because of this, the solidpolymeric electrolyte film 114 is preferably a film with the highhydrogen ion conductivity. Moreover, it is preferably a chemicallystable film with a high mechanical strength.

A material comprising the solid polymeric electrolyte film 114 includesthe organic polymers having polar groups such as strongly acidic groupssuch as sulfone group, phosphate group, phosphone group, and phosphinegroup; and a weakly acidic groups such as carboxyl group. The typicaland preferred examples of the organic polymers having polar groups suchas these include: an aromatic group containing high molecules such assulfonation of poly (4-phenoxybenzoyl-1,4-phenylene), and alkylsulfonation polybenzimidazole; polystyrene sulfonate copolymer,polyvinylsulfonate copolymer, and copolymer such as fluoride containinghigh molecules consisting of bridging alkyl sulfonate derivative,fluoride resin structure, and sulfonate; copolymer obtained bycopolymerization of acrylate group such as n-butyl methacrylate andacrylamide group such as acrylamide-2-methyl-propane-sulfonate; sulfonegroup containing perfluorocarbon such as Nafion® (Du Pont) and Aciplex®(Asahi Kasei); and carboxyl group containing perfluorocarbon such asFlemion® S-film (Asahi Glass). It should be noted that the examples arenot necessarily limited to these. Among these, if aromatic groupcontaining high molecules such as sulfonation of poly(4-phenoxybenzoyl-1,4-phenylene) and alkyl sulfonation polybenzimidazoleare selected, the permeation of liquid organic fuel is controlled, anddecline in the cell efficiency due to cross-over is suppressed.

As for both substrates 104 and 110 of the fuel electrode 102 and theoxidizing agent electrode 108, respectively, the porous substrate suchas carbon paper, carbon shape, sintered carbon, sintered metal, andfoamed metal can be utilized. Moreover, as for the water-repellingprocess of the substrate, water repellent agent such aspolytetrafluoroethylene is utilized.

The typical examples of catalysts of the fuel electrode 102 areplatinum, rhodium, palladium, iridium, osmium, ruthenium, rhenium, gold,silver, nickel, cobalt, lithium, lanthanum, strontium, and yttrium.However, examples are not necessarily limited to these. The catalystsindicated above can be used alone or in combination or more than twotypes.

On the other hand, as a catalyst of the oxidizing agent electrode 108,the same catalyst as the fuel electrode 102 can be utilized, and theabove examples can be used. Note that the same catalyst can be used asthe catalysts of the fuel electrode and the oxidizing agent electrode,alternatively, different catalysts can be used.

Moreover, examples of carbon powders for supporting the catalysts areacetylene black (such as Denka Black® (Denki Kagaku Kogyo) XC72 (Vulcan)), ketjen black, carbon nano tube, and carbon nanohorn. Particlediameter of carbon powders, for example, is 0.01 to 0.1 μm, and morepreferably 0.02 to 0.06 μm.

Moreover, a liquid organic fuel having a C—H bond is preferably used asa fuel. Typical examples of liquid organic fuel having the C—H bondincludes: alcohol groups such as methanol, ethanol, and propanol; ethergroups such as dimethylether; cyclo parafin groups such as cyclo hexane;cyclo parafin groups having hydrophilic group such as hydroxyl group,carboxyl group, amino group, and amide group; and monosubstituted ordisubstituted cyclo parafin. However, the examples are not necessarilylimited to these. Herewith, the cyclo parafin groups refer to cycloparafins and their substitute besides the aromatic compounds.

In the fuel for the fuel cell of the present invention, for the purposeof generating an osmotic pressure, a compound not permeating the solidpolymeric electrolyte film 114 is dissolved. By doing so, at aninterface between the solid polymeric electrolyte film 114 and the fuel124 in the fuel electrode 102, an osmotic pressure is stably generatedin a direction from the oxidizing agent electrode 108 to the fuelelectrode 102, and water movement from the fuel electrode 102 to theoxidizing agent electrode 108 is controlled. Due to the water movementcontrolled, the liquid organic fuel movement from the fuel electrodeside to the oxidizing agent electrode side is decreased. Accordingly,the problem of cross-over is improved, and the cell efficiency is alsoimproved.

Moreover, in order to generate the osmotic pressure stably, thesecompounds are preferably electrochemically inert, and furthermore,preferably volatile.

These compounds can be dissolved into the liquid organic fuelbeforehand. Moreover, these compounds can be added to the liquid organicfuels immediately before operating the fuel cell.

Examples of the compounds satisfying these conditions above are thestrong electrolytes and the organic compounds.

Typical examples of strong electrolytes include NaCl, KCl, NaNO3,NH4NO3, Na2SO4, K2SO4, (NH4)2SO4, NaHCO3, KHCO3, however, the examplesare not necessarily limited to these.

The strong electrolyte is dissolved to a liquid organic fuel byseparating to the positive ion and negative ion. Because of this, in theliquid organic fuel, single-molecule strong electrolyte acts asdouble-molecules or triple-molecules, hence a high osmotic pressure canbe generated by small amount of addition.

The strong electrolyte has an effect of improving the hydrogen ionconductivity of the liquid organic fuel, therefore, an inner resistanceof the cell is suppressed. Accordingly, the cell output is increased.

Herewith, the sulfuric acid (H2SO4) is a strong electrolyte, however, itis avoided from being selected as the compound. The sulfuric acid isstrongly corrosive, and prominently deteriorates the metallic componentsinside the fuel cell, causing difficulty in supporting the long-termreliability of the fuel cell. Moreover, the sulfuric acid isnon-volatile, and it may cause a bad influence on human skin structuresuch as damages and inflammations. Considering the safety factors uponfuel leakage and to be cautious upon handling the fuel, the sulfuricacid is not an ideal selection.

Examples of organic compounds are sugar groups, alcohol groups, andamine groups having hydrophilic properties.

Typical examples of sugar groups are sugars such as glyceraldehyde,dihydroxy-acetone, ribose, deoxyribose, xylose, arabinose, glucose,fructose, and galactose; sugar alcohol groups such as sorbitol,mannitol, and inositol; and amino sugar groups such as glucosamine andchondroitin. However, examples are not necessarily limited to these.Moreover, a plurality of the sugar groups listed above may be combinedto form disaccharides, trisaccharides, and polysaccharides which arealso usable.

Typical examples of alcohol groups are alcohol groups of more than 3carbon atoms, for instance, a high-grade alcohol group such as heptanol,heptanediol, heptanetriol, octanol, octanediol, nonanol, nonanediol, andisononanol; cyclo aliphatic alcohol groups such as cyclo heptanol andcyclo nonanediol; polycyclic aliphatic alcohol of more than dicyclic;and compounds containing ethyl bond such as diethylene glycol. However,the examples are not necessarily limited to these.

Typical examples of amine groups are amine groups having more than 3carbon atoms, for instances: aliphatic amine groups such as propanamine,diethylamine, triethylamine, tributylamine, butanamine; cyclic aminegroups such as pyrrolidine, piperidin, piperazine, and morpholine.However, the examples are not necessarily limited to these.

Concentration of the compound above in the liquid organic fuel isranging from 0.1 mmol/L to 5 mol/L, and more preferably is ranging from1 mmol/L to 1 mol/L. This way, a sufficient osmotic pressure necessaryto decrease the cross-over is possible.

Now, the fuel for the fuel cell dissolving the above compound preferablyhas the pH value ranging from 4 to 8. To provide the hydrogen ionconductivity, the solid electrolyte film keeps an acidic state. If thefuel is strongly alkaline, a neutralization reaction occurs inside thesolid electrolyte film, and the hydrogen ion conductivity is lost.Accordingly, to avoid losing of the hydrogen ion conductivity, the pHvalue of the fuel for fuel cell is set in the range of 4 to 8. This way,it becomes possible to generate the osmotic pressure without inhibitingthe operation of the fuel cell. Furthermore, if the pH of the fuel is inthe range of 4 to 8, a highly reliable fuel cell is provided, withoutgiving a bad influence such as corrosion of the metallic components suchas current collector, electrode, or metallic seal.

From the following notions, either one of strong electrolyte compound ororganic compound is preferably selected. The strong electrolyte ispreferable from the notion of increasing the hydrogen ion conductivity.If the unit cells are connected in series, and the voltage of wholecells is more than 1 V, the water electrolysis is generated. Under suchcircumstance, the electrolyte is not adopted, and instead, the organiccompounds mentioned above can be utilized. This way, the liquidresistance of fuel is appropriately maintained high, and the osmoticpressure is generated without generating the water electrolysis.

The production method of the fuel electrode 102 and the oxidizing agentelectrode 108 of the present invention is not particularly limited.Followings are some of the production examples.

First of all, the catalyst support of the carbon powders for the fuelelectrode 102 and the oxidizing agent electrode 108 is performed bygenerally adopted impregnation method. Then, the carbon powderssupporting the catalyst and the solid polymeric electrolyte powders aredispersed in a solvent, and after forming a paste, it is coated to thesubstrate, drying it, and the fuel electrode 102 and the oxidizing agentelectrode 108 are obtained accordingly. Herewith, a particle diameter ofcarbon powders, for example, is ranging from 0.01 to 0.1 μm. A particlediameter of catalyst powders, for example, is ranging from 1 nm to 10nm. A particle diameter of solid polymeric electrolyte powders, forexample, is ranging from 0.05 to 1 μm. Weight ratio of the carbonpowders and the solid polymeric electrolyte powders, for example, isranging from 2:1 to 40:1. Moreover, weight ratio of water inside thepaste and solvent, for example, is ranging from 1:2 to 10:1. Coatingmethod of the paste to the substrate is not particularly limited, forexample, brushing, spraying, and screen printing methods can beutilized. The paste is coated at the thickness of approximately 1 μm to2 mm. After the paste is coated, the coated substrate is heated attemperature and heating time depending on the fluoride resin in use, andthe fuel electrode 102 and the oxidizing agent electrode 108 areproduced accordingly. The heating time and temperature are appropriatelyselected depending on the material in use, for example, the temperatureof 100° C. to 250° C., and the heating time of 30 seconds to 30 minutes.

The solid polymeric electrolyte film 114 of the present invention isproduced by adopting an appropriate method depending on the material inuse. For example, if the solid polymeric electrolyte film 114 iscomprised of an organic polymer material, a liquid having dissolved ordispersed an organic polymer material to a solvent is obtained bycasting on the detachable sheet such as polytetrafluoroethylene, anddrying it.

The solid polymeric electrolyte film 114 produced accordingly issandwiched by the fuel electrode 102 and the oxidizing agent electrode108, it is hot-pressed, and the electrode and electrolyte assembly 101is obtained. At this time, on the faces where the catalyst is preparedfor both electrodes and the solid polymeric electrolyte film 114 shouldcome in contact to one another. The hot pressing condition is selecteddepending on the material. If the solid polymeric electrolyte film 114and the electrolyte film of the electrode surface is constituted withthe organic polymer, the temperature exceeding the softening temperatureand the glass transition temperature of these polymers can be used.Specifically, for example, the temperature of 100 to 250° C., thepressure of 5 to 100 kgf/cm2, and the time of 10 seconds to 300 seconds.

Herewith, the liquid organic fuel that did not react in the fuelelectrode is recycled, and it can be used again. Such example shall bedescribed with reference to FIG. 3.

Referring to FIG. 3, the detail of the fuel cell 100 is omitted beingsame as FIG. 1. According to the embodiment, a fuel supplying systemcomprises a fuel supplying section 313 for supplying a fuel to the fuelelectrode of the fuel cell; a fuel recycling section 314 for recyclingthe used fuel expelled from the fuel electrode of the fuel cell; aconcentration detecting section 315 for measuring concentrations of thecompound and a liquid organic fuel in the used liquid fuel; and aconcentration adjusting section 316 for adjusting concentrations of thecompound and the liquid organic fuel in the used liquid fuel. Moreover,the fuel moves in the direction of the arrow in the drawing by theliquid transport mechanism which is not illustrated.

The fuel is supplied to the fuel electrode of the fuel cell 100 by thefuel supplying section 313. After passing through the fuel electrode,the fuel is recycled at the fuel recycling section 314. A substancegenerated by the electrode reaction at the fuel electrode, such ascarbon dioxide, is separated at the fuel recycling section 314. Next,the recycled fuel is sent to the fuel detecting section 315 whereconcentrations of the compound and liquid organic fuel are measured.Based on the measured results, the concentrations of the compound andthe liquid organic fuel are appropriately adjusted, and regenerated as afuel. The fuel regenerated accordingly is sent to the fuel supplyingsection 313, and sent to the fuel electrode of the fuel cell 100.

The fuel cell that efficiently uses a fuel is implemented by comprisingthe fuel supplying system described accordingly.

EMBODIMENTS

Hereinafter, the electrodes of the solid polymeric type fuel cellelectrode and the fuel cell using them related to the present inventionshall be specifically described according to the embodiments, however,it should be understood that the present invention is not necessarilylimited to these.

Embodiment 1

The fuel cell according to the present embodiment shall be describedwith reference to FIG. 2.

First of all, in the fuel electrode 102 and the oxidizing agentelectrode 108, 500 g of dinitro diammine platinum nitrate solutioncontaining 3% platinum as catalyst and 10 g of acetylene black (DenkaBlack®; Denki Kagaku Kogyo) are mixed and agitated. As reducing agent,60 mL of ethanol 98% is added. The mixed solution is agitated atapproximately 95° C. for 8 hours so that the catalyst substance andplatinum fine powders are supporting the acetylene black powders. Then,the mixed solution is filtered, dried, and catalyst supporting carbonpowders are obtained. The supporting amount of platinum is about 50% inrespect to the weight of acetylene black.

Next, 200 mg of the catalyst supporting carbon powders and 3.5 mL ofNaifon® solution 5% (alcohol solution; Aldrich Chemicals) is mixed andagitated. This way, Nafion® is deposited on the surfaces of carbonpowders and catalyst. The dispersed solution obtained accordingly isdispersed in the ultrasonic homogenizer for 30 hours at 50° C., and apaste is formed. The paste is coated on the carbon paper (TGP-H-120;Toray) using the screen printing method at 2 mg/cm2, and dried at 120°C., and the electrode is obtained accordingly.

As the solid polymeric electrolyte film 114, Nafion 117® (thickness 150μm) of DuPont is utilized. The electrode obtained accordingly is hotpressed at 120° C. to the solid polymeric electrolyte film 114, and thefuel electrode 102 and the oxidizing agent electrode 108 are obtained.

The solid polymeric electrolyte film 114 is sandwiched by theseelectrodes, and the electrode and electrolyte assembly 101 is producedby hot pressing at the condition of 150° C. temperature, 10 kgf/cm2pressure, and 10 seconds.

For supplying a fuel to the fuel electrode 102, a fuel flow duct 311made of tetrafluoroethylene resin is prepared on top of the fuelelectrode 102. To the fuel flow duct 311, a fuel tank 307 and a liquidwaste tank 308 are prepared. A pump is equipped to the fuel tank 307. Asindicated by the arrows in the drawing, the configuration shows themethanol is continuously being supplied to the fuel electrode 102.

Moreover, for supplying an oxidizing agent to the oxidizing agentelectrode 108, an oxidizing agent flow duct 312 made oftetrafluroethylene resin is prepared on top of the oxidizing agentelectrode 108. To the oxidizing flow duct 312, an oxygen compressor 309and an exhaust outlet 310 are prepared. As indicated by the arrows inthe drawing, the configuration shows the oxygen is continuously beingsupplied to the oxidizing agent electrode 108.

A fuel dissolving diethylene-glycol to 10 weight % of methanol solutionis poured into the fuel tank 307. Note that the concentration ofdiethylene-glycol of the fuel is 0.1 mol/L. This fuel is supplied to thefuel electrode 102 at 2 mL/min.

As for the oxidizing agent electrode 108, the oxygen of 1.1 atmosphericpressure at 25° C. is supplied by the oxygen compressor 309. Under theseoperating conditions the current and voltage characteristics of the unitcell are measured.

Embodiment 2

A fuel dissolving glucose is poured into 10 weight % methanol solutionas a fuel to be poured into the fuel tank 307 of the fuel cell havingthe same configuration as Embodiment 1. The glucose concentration ofthis fuel is 0.1 mol/L. The fuel is supplied to the fuel electrode 102at 2 mL/min. As for the oxygen, the condition is same as Embodiment 1.Under these operating conditions, the current and voltagecharacteristics of the unit cell are measured.

Embodiment 3

A fuel dissolving NaCl is poured into 10 weight % methanol solution as afuel to be poured into the fuel tank 307 of the fuel cell having thesame configuration as Embodiment 1. The NaCl concentration of this fuelis 0.1 mol/L. The fuel is supplied to the fuel electrode 102 at 2mL/min. As for the oxygen, the condition is same as Embodiment 1.

Under these operating conditions, the current and voltagecharacteristics of the unit cell are measured.

Comparative Example 1

10 weight % methanol solution is used as a fuel to be poured into thefuel tank 307 of the fuel cell having the same configuration asEmbodiment 1. The fuel is supplied to the fuel electrode 102 at 2mL/min. As for the oxygen, the condition is same as Embodiment 1.

Under these operating conditions, the current and voltagecharacteristics of the unit cell are measured.

Measured results of the current and voltage characteristics of fuelcells of Embodiments 1 to 3, and the comparative example 1 are shown intable 1. TABLE 1 Open circuit Short circuit Max. power voltage (V)current (mA/cm²) (mW/cm²) Embodiment 1 0.64 260 39 Embodiment 2 0.65 28049 Embodiment 3 0.66 330 54 Comparative 0.6 200 33 Example

Unit cells of Embodiments 1 to 3, compared to the unit cell of thecomparative example, all of the open circuit voltage, the short circuitcurrent, and the maximum power are found to be excellent. This isconsidered to have the following reasons.

As for the unit cells of Embodiments 1 to 3, diethylene glycol orglucose or NaCl is dissolved into the fuel, therefore, at the interfaceof fuel present in the fuel electrode 102 and the solid polymericelectrolyte film 114, an osmotic pressure in a direction from theoxidizing agent side to the fuel electrode side occurs. Because of this,the movement of water molecules in a direction from the fuel electrodeto the oxidizing agent electrode is controlled, the cross-over ofmethanol is considered to had decreased.

Particularly, as for the unit cell of Embodiment 3, a single molecule ofNaCl is dissociated to Na+ and Cl—and acts as two molecules, therefore,a larger osmotic pressure is thought to have been generated than theunit cells of Embodiments 1 and 2. Moreover, as for the unit cell ofEmbodiment 3, the fuel conductivity is high because the strongelectrolyte is being dissolved into the fuel. This contributes to thereduction of inner resistance of the unit cell. Consequently, as aresult, the performance of unit cell of Embodiment 3 is most superior.

INDUSTRIAL APPLICABILITY

According to the present invention as described above, the cross-over ofthe liquid organic fuel is controlled, and the high fuel efficiency andthe high output of the fuel cell is implemented.

1. A fuel for solid electrolyte type fuel cell having a solidelectrolyte film, wherein the fuel includes a liquid organic fuel, and acompound excluding the sulfuric acid dissolved in the liquid organicfuel and does not permeate the solid electrolyte film.
 2. The fuel forsolid electrolyte type fuel cell according to claim 1, wherein thecompound is non-electrolyte.
 3. The fuel for solid electrolyte type fuelcell according to claim 1, wherein the compound is an organic compounddifferent from the liquid organic fuel.
 4. The fuel for solidelectrolyte type fuel cell according to claim 3, wherein the organiccompound is selected from at least one of sugers, alcohols and amines.5. The fuel for solid electrolyte type fuel cell according to claim 1,wherein the compound is a strong electrolyte.
 6. The fuel for solidelectrolyte type fuel cell according to claim 5, wherein the strongelectrolyte is chloride, nitrate, and sulfate.
 7. The fuel for solidelectrolyte type fuel cell according to claim 1, wherein the compoundhas a concentration ranging from 0.1 mmol/L to 5 mol/L.
 8. The fuel forsolid electrolyte type fuel cell according to claim 1, wherein thecompound has a concentration ranging from 1 mmol/L to 1 mol/L.
 9. Thefuel for solid electrolyte type fuel cell according to claim 1, whereinthe fuel has a pH value ranging from 4 to
 8. 10. The fuel for solidelectrolyte type fuel cell according to claim 1, wherein the compound iselectrochemically inert and non-volatile.
 11. A method of using thesolid electrolyte type fuel cell comprising a fuel electrode, anoxidizing agent electrode, and a solid electrolyte film positioned inbetween the fuel electrode and the oxidizing agent electrode; whereinthe fuel includes a liquid organic fuel and a compound excluding thesulfuric acid dissolved in the liquid organic fuel and does not permeatethe solid electrolyte film, which is supplied to the fuel electrode. 12.The method of using the solid electrolyte type fuel cell according toclaim 11, wherein the compound is non-electrolyte.
 13. The method ofusing the solid electrolyte type fuel cell according to claim 11,wherein the compound is an organic compound different from the liquidorganic fuel.
 14. The method of using the solid electrolyte type fuelcell according to claim 13, wherein the organic compound is selectedfrom at least one of sugers, alcohols, and amines.
 15. The method ofusing the solid electrolyte type fuel cell according to claim 11,wherein the compound is a strong electrolyte.
 16. The method of usingthe solid electrolyte type fuel cell according to claim 15, wherein thestrong electrolyte is a chloride, nitrate, and sulfate.
 17. The methodof using the solid electrolyte type fuel cell according to claim 11,wherein the compound has a concentration ranging from 0.1 mmol/L to 5mol/L.
 18. The method of using the solid electrolyte type fuel cellaccording to claim 11, wherein the compound has a concentration rangingfrom 1 mmol/L to 1 mol/L.
 19. The method of using the solid electrolytetype fuel cell according to claim 11, wherein the fuel has a pH valueranging from 4 to
 8. 20. The method of using the solid electrolyte typefuel cell according to claim 11, wherein the compound iselectrochemically inert and non-volatile.
 21. A solid electrolyte typefuel cell, comprising: a fuel electrode; an oxidizing agent electrode; asolid electrolyte film positioned in between the fuel electrode and theoxidizing agent electrode; and a solid electrolyte type fuel cell thatincludes a fuel supplied to the fuel electrode, wherein the fuelincludes a liquid organic fuel, and a compound excluding the sulfuricacid dissolved in the liquid organic fuel and does not permeate thesolid electrolyte film.
 22. The solid electrolyte type fuel cellaccording to claim 21, further comprising a supplying step for supplyingthe fuel to the fuel electrode.
 23. The solid electrolyte type fuel cellaccording to claim 22, further comprising a recycling step for recyclinga fuel expelled from the fuel electrode; a concentration adjusting stepfor adjusting a concentration of the compound, and the liquid organicfuel inside a recycled fuel at the recycling step; and a transportingstep for transporting the fuel to the supplying step of which aconcentration is adjusted by the concentration adjusting step.
 24. Thesolid electrolyte type fuel cell according to claim 21, wherein thecompound is a non-electrolyte.
 25. The solid electrolyte type fuel cellaccording to claim 21, wherein the compound is an organic compounddifferent from the liquid organic fuel.
 26. The solid electrolyte typefuel cell according to claim 25, wherein the organic compound isselected from at least one of sugers, alcohols, and amines.
 27. Thesolid electrolyte type fuel cell according to claim 21, wherein thecompound is a strong electrolyte.
 28. The solid electrolyte type fuelcell according to claim 27, wherein the strong electrolyte is chloride,nitrate, and sulfate.
 29. The solid electrolyte type fuel cell accordingto claim 21, wherein the compound has a concentration ranging from 0.1mmol/L to 5 mol/L.
 30. The solid electrolyte type fuel cell according toclaim 29, wherein the compound has a concentration ranging from 1 mmol/Lto 1 mol/L.
 31. The solid electrolyte type fuel cell according to claim21, wherein the fuel has a pH value ranging from 4 to
 8. 32. The solidelectrolyte type fuel cell according to claim 21, wherein the compoundis electrochemically inert and non-volatile.